Sponge City: Environment Friendly Answer to Urban Flooding

Urban flooding is a severe problem in many parts of the world. It is a major concern in Asian countries which are facing rapid urbanization. Some countries have already started taking action. The Chinese government, in its effort to counter the issue of urban flooding, is planning to build 30 sponge cities.

Before we understand the concept of sponge cities and how they can solve urban flooding, we need to understand the cause of urban flooding first.

Why urban flooding occurs?

Urban flooding occurs because most human-built structures are impervious to water, so water can’t seep through in the ground. So, when it rains, the only point of exit for rainwater is storm drain, through which the rainwater moves to the sewers. Then through the sewer, rainwater moves out of the city. But, when it rains heavily, the intake capacity of storm drains and sewers is overwhelmed. The result is flooding. As cities need to expand, they are often forced into low lying areas, which previously used to hold or had the capacity to hold stormwater. Another important factor is global warming and climate change, due to which sudden and unexpected rains have increased in recent years.

What is a Sponge City?

Sponge city is a city which is designed in a way that the rainwater is either absorbed into the soil or used directly by humans. For achieving this, rooftop gardens are added to the buildings. Green spaces are increased by creating parks, adding greenery on the side of roads. When it rains, rooftop gardens and other green spaces absorb the amount of rainwater they could. Excess rainwater is channeled towards man-made wetlands, where they stay for longer periods of time and are slowly absorbed into the soil as groundwater.

What are the benefits of a Sponge City?

Modern cities work against nature, they absorb heat and are impervious to water. Sponge city reverses that. It absorbs water and makes the surroundings cooler. Since a sponge city doesn’t pipe away the rainwater, the excess rainwater can be reused by humans (China plans to use 70% of the rainwater in its sponge cities). A sponge city also helps in increasing groundwater level. As a sponge city has a lot of trees and plants, it absorbs CO2 and particulates from the air, making the air more breathable. Hence, it also helps in reducing global warming. Green spaces create a microclimate, which means that the summer is a little bit less warm than the surrounding.

Global warming and climate change is taking a heavy toll on every part of the world. But, the rapidly developing and countries in Asia and Africa, which are also facing rapid and sometimes poorly planned urbanization are especially hit hard. One of the countries hit most hard is China, that’s why China is going so far in its bid to fight climate change. China is already building a forest city in Liuzhou, has completed a floating solar power plant among many other projects. Now, China is experimenting with sponge cities, with a plan to develop 30 of them, with a budget of $12 billion.

What next to sponge cities?

Sponge cities, although a good start, are not the ultimate solution. City planners all around the world should continue to add sponge city characteristics to existing cities, and also develop new cities accordingly. But, the fight against global warming and climate change doesn’t even here. We need to continue the electrification of transportation (beyond cars to ships, aircrafts), increase the share of renewable resources in electricity generation, invent new eco-friendly methods and use the existing ones, then only we can win this war against global warming and climate change.